I have a piece of openmp code for testing scaling of mutithreads:

void  openmp_scalabity_test ()
{
  
    int tid ;
    
    omp_set_num_threads(numberofthreads);  // here I specify the number of threads: 
    double t0, t1;
    
    #pragma omp parallel private(tid, t0, t1)
    {
      
        t0 = MPI_Wtime();

        #pragma omp for
        for(std::size_t zindex=0; zindex<10000000000; zindex++)     
        {
                 
                    tid = omp_get_thread_num();

         }      
  
        t1 = MPI_Wtime(); 

        #pragma omp barrier 
        if(tid==0)
        {
            std::cout <<" Multithread wall clock: "<<t1-t0<<" in threads: " << omp_get_thread_num()<<std::endl;
        }
        
    }
}

I run the code by mpi,

mpirun --bind-to none -np 1 ./test

My CPU info as follows:

rchitecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          46 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   24
  On-line CPU(s) list:    0-23
Vendor ID:                GenuineIntel
  Model name:             12th Gen Intel(R) Core(TM) i9-12900K
    CPU family:           6
    Model:                151
    Thread(s) per core:   2
    Core(s) per socket:   16
    Socket(s):            1
    Stepping:             2
    CPU(s) scaling MHz:   17%
    CPU max MHz:          5200.0000
    CPU min MHz:          800.0000
    BogoMIPS:             6374.40

Here is bit confusing for me. It seems I have 16 cores, and each core has 2 threads. I expect that I can get good scaling up to 32 threads.

However, here is the time for the test:

1 threads:  3.93
2 threads:  2.01
4 threads:  1.04
8 threads:  0.56
16 threads: 0.58
32 threads: 0.63

It seems I can only get good scaling up to 8 threads.